Nice one.. Good find.
On Sat, Mar 30, 2013 at 12:30 AM, Ted Yu <yuzhih...@gmail.com> wrote:
> Can you tell us the version of HBase you are using ?
>
> Gary did some cleanup in:
>
> r1439723 | garyh | 2013-01-28 16:50:02 -0800 (Mon, 28 Jan 2013) | 1 line
>
> HBASE-7626 Backport client connection cleanup from HBASE-7460
>
> This is the current code in getConnection() in 0.94 branch:
> ConnectionId remoteId = new ConnectionId(addr, protocol, ticket,
> rpcTimeout);
> synchronized (connections) {
> connection = connections.get(remoteId);
> if (connection == null) {
> connection = createConnection(remoteId);
> connections.put(remoteId, connection);
> }
> }
> connection.addCall(call);
>
>
> On Fri, Mar 29, 2013 at 11:41 AM, Jeff Whiting <je...@qualtrics.com>
> wrote:
>
> > After noticing a lot of threads, I turned on debugging logging for hbase
> > client and saw this many times counting up constantly:
> > HBaseClient:531 - IPC Client (687163870) connection to
> > /10.1.37.21:60020from jeff: starting, having connections 1364
> >
> > At that point in my code it was up to 1364 different connections (and
> > threads). Those connections will eventually drop off after the idle time
> > is reached "conf.getInt("hbase.ipc.client.connection.maxidletime",
> 10000)".
> > But during periods of activity the number of threads can get very high.
> >
> > Additionally I was able to confirm the large number of threads by doing:
> >
> > jstack <pid> | grep IPC
> >
> >
> > So I started digging around in the code...
> >
> > In HBaseClient.getConnection it attempts to reuse previous connections:
> >
> > ConnectionId remoteId = new ConnectionId(addr, protocol, ticket,
> > rpcTimeout);
> > do {
> > synchronized (connections) {
> > connection = connections.get(remoteId);
> > if (connection == null) {
> > LOG.error("poolsize: "+getPoolSize(conf));
> > connection = new Connection(remoteId);
> > connections.put(remoteId, connection);
> > }
> > }
> > } while (!connection.addCall(call));
> >
> >
> > It does this by using the connection id as the key to the pool. All of
> this
> > seems good except ConnectionId never hashes to the same value so it
> cannot
> > reuse any connection.
> >
> > From my understanding of the code here is why.
> >
> > In HBaseClient.ConnectionId
> >
> > @Override
> > public boolean equals(Object obj) {
> > if (obj instanceof ConnectionId) {
> > ConnectionId id = (ConnectionId) obj;
> > return address.equals(id.address) && protocol == id.protocol &&
> > ((ticket != null && ticket.equals(id.ticket)) ||
> > (ticket == id.ticket)) && rpcTimeout == id.rpcTimeout;
> > }
> > return false;
> > }
> >
> > @Override // simply use the default Object#hashcode() ?
> > public int hashCode() {
> > return (address.hashCode() + PRIME * (
> > PRIME * System.identityHashCode(protocol) ^
> > (ticket == null ? 0 : ticket.hashCode()) )) ^ rpcTimeout;
> > }
> >
> > It uses the protocol and the ticket in the both functions. However going
> > back through all of the layers I think I found the problem.
> >
> > Problem:
> >
> > HBaseRPC.java: public static VersionedProtocol getProxy(Class<? extends
> > VersionedProtocol> protocol,
> > long clientVersion, InetSocketAddress addr, Configuration conf,
> > SocketFactory factory, int rpcTimeout) throws IOException {
> > return getProxy(protocol, clientVersion, addr,
> > User.getCurrent(), conf, factory, rpcTimeout);
> > }
> >
> > User.getCurrent() always returns a new User object. That user instance
> is
> > eventually passed down to ConnectionId. However the User object doesn't
> > implement hash() or equals() so one ConnectionId won't ever match another
> > ConnectionId.
> >
> >
> > There are several possible solutions.
> > 1. implement hashCode and equals for the User.
> > 2. only create one User object and reuse it.
> > 3. don't look at ticket in ConnectionId (probably a bad idea)
> >
> >
> > Thoughts? Has anyone else noticed this behavior? Should I open up a
> jira
> > issue?
> >
> > I originally ran into the problem due to OS X having a limited number of
> > threads per user (and I was not able to increase the limit) and our unit
> > tests making requests quick enough that I ran out of threads. I tried
> out
> > all three solutions and it worked fine for my application. However I'm
> not
> > sure what changing the behavior would do to other's applications
> especially
> > those that use SecureHadoop.
> >
> >
> >
> > Thanks,
> > ~Jeff
> >
> > --
> > Jeff Whiting
> > Qualtrics Senior Software Engineer
> > je...@qualtrics.com
> >
>
